Full duplex systems have the ability to simultaneously transmit and receive signals on a single channel. If the self-interference of a wireless network can be reduced, a system's own transmissions will not interfere with incoming packets. In addition to analog and digital techniques, antenna placement is used as an additional cancellation technique to minimize self-interference. However, there are many limitations to these techniques. Antenna placement techniques take advantage of the fact that distances naturally reduce self-interference, but impractically large distances are required to achieve enough reduction through antenna placement alone.
To further cancel self-interference, an additional technique, called antenna cancellation may be used. Antenna cancellation combined with other mechanisms, allows for full duplex operation. Antenna cancellation-based designs have three major limitations. The first limitation is that they require three antennas (two transmit, one receive). The second limitation is a bandwidth constraint, a theoretical limit which prevents supporting wideband signals such as WiFi. The third limitation is that it requires manual tuning. Manual tuning is sufficient for lab experiments, but it brings into question whether a full duplex system can automatically adapt to realistic, real world environments.
Balun cancellation uses signal inversion, through a balun circuit. Balun cancellation has no bandwidth constraint. It requires only two antennas, one transmit and one receive. A tuning algorithm exists that allows a balun-based radio design to quickly, accurately, and automatically adapt the full duplex circuitry to cancel the primary self-interference component.